As outlined, the fill unit delivers the fill material under pressure into the feeder tube at the hookup. The fill material is transported or conducted through the feeder tube to the closing unit. The casing moves over the outer surface of the feeder tube toward the closing unit. Adjacent to the closing unit, the fill material emerges from the feeder tube mouth and fills the casing, which is sealed with a clip at the leading end. Once the specified or desired fill portion is reached, constricting elements in the closing unit partition off the stuffed casing, thus creating an empty, collapsed casing segment for the sausage end. Usually, two sealing clips are placed one after the other around the collapsed casing at the sausage end and closed using punching tools. Now, the casing may be cut with a knife between sealing clips.
It is also known how to make the required casings for sausages or similarly packaged items on site as part of the packaging process. The methods involve forming the plastic filmstrip and then closing the longitudinal seam either continuously or intermittently using a sealing device. An example of such a sealing method is known from European patent EP 0 908 103 A1, in which a feeder mechanism first pushes the plastic film strip over a forming pad and then pulls it through a sealing device. The forming pad encircles the feeder tube and covers a short section of it with the plastic filmstrip in such a way that its longitudinal edges either meet each other flush or overlap. The sealing device fuses overlapping plastic film edges directly, in cases where the longitudinal edges meet flush, a sealing band that covers the adjoining edges is added before the fusion process. Sealing is defined as forming any permanent seal between the longitudinal edges of the plastic filmstrip. This may, for example, be accomplished through the preferred fusion method or alternatively, also through bonding.
The casing is formed in the above-described way as a quasi-endless plastic film tube. Infeed drives then push the tube forward over the feeder tube to a segment where a casing supply accumulates (bunches up) in harmonica folds. There has to be an excess casing supply when the sealing process (continuous or intermittent) is slower than the filling process, during which the forced output of filling intermittently pulls the casing off the feeder tube.
Other known versions of sealing devices do not require an infeed drive because there are no extra folds of casing supply. With these devices, the casing is consecutively sealed and filled in a synchronized rhythm. During the fill process, the forced output of filling directly pulls the casing off the feeder tube, while the sealing device is on standby.
Still longer known in sausage making are methods, in which the required supply of ready-made casing is manually pushed onto the outer feeder tube from its mouth end, e.g. in harmonica-like folds. Through the filling output, the required length of the casing is pulled off the feeder tube against the friction from the brake ring of a retaining device. Once exhausted, new casing must be supplied. To apply the new casing, the feeder tube is pivoted out from its operating/fill position gain free access to the feeder tube mouth. Even today, casing is applied to the feeder tube in this way when it is not cost-effective to produce the casing continuously from plastic filmstrips, e.g. when using natural casing or when producing small quantities of sausages of variable caliber.